Polysaccharide vaccines, when prepared without carrier protein, lack immune memory responses. Currently known conjugated vaccines include bacterial capsular polysaccharides such as Haemophilus influenzae type b, Neisseria meningitidis group C, and Streptococcus pnemoniae serotypes 1, 3, 4, 5, 6B, 7F, 9V, 14, 19F, 23F. These vaccines are covalently conjugated to a carrier protein, such as tetanus toxoid, diphtheria toxoid, CRM197, a mutant nontoxic diphtheria toxin, or Neisseria meningitidis outer membrane protein. These polysaccharide conjugate vaccines could induce T-cell dependent response, especially in infants below the age of two years; and they could prime long term immunologic memory, produce high affinity antibody, and could lower the rate of nasopharyngeal colonization and transmission.
However, the majority of the currently marketed bacterial polysaccharide conjugate vaccines applied tetanus toxoid (TT) or diphtheria toxoid (DT) as a carrier protein. TT and DT, these two toxoid proteins, are regular vaccines for infants/children; high frequency vaccination of TT and DT within a short time could have impact on the immunogenicity and safety. (Reduced response to multiple vaccines sharing common protein epitopes that are administered simultaneously to infants. Infect. Immun. 1998; 66(5):2093-8; Immunogenicity and safety of a combination pneumococcal-meningococcal vaccine in infants: a randomized controlled trial. JAMA 2005; 293(14):1751-8). Therefore, this invention provides a new type of the carrier protein LTS61K for its use on the conjugate vaccine.